Programming language: Python
License: MIT License
Tags: Serialization    
Latest version: v1.5.0

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Quick-n'dirty Python bindings for simdjson just to see if going down this path might yield some parse time improvements in real-world applications. So far, the results are promising, especially when only part of a document is of interest.

Bindings are currently tested on OS X, Linux, and Windows.

See the latest documentation at http://pysimdjson.tkte.ch.


There are binary wheels available for some platforms. On other platforms you'll need a C++17-capable compiler.

pip install pysimdjson

Binary wheels are available for:

Platform py3.4 py3.5 py3.6 py3.7
OS X 10.12 x x x y
Windows x x y y
Linux y y y y

or build from git:

git clone https://github.com/TkTech/pysimdjson.git
cd pysimdjson
python setup.py install


import simdjson

with open('sample.json', 'rb') as fin:
    doc = simdjson.loads(fin.read())

However, this doesn't really gain you that much over, say, ujson. You're still loading the entire document and converting the entire thing into a series of Python objects which is very expensive. You can instead use items() to pull only part of a document into Python.

Example document:

    "type": "search_results",
    "count": 2,
    "results": [
        {"username": "bob"},
        {"username": "tod"}
    "error": {
        "message": "All good captain"

And now lets try some queries...

import simdjson

with open('sample.json', 'rb') as fin:
    # Calling ParsedJson with a document is a shortcut for
    # calling pj.allocate_capacity(<size>) and pj.parse(<doc>). If you're
    # parsing many JSON documents of similar sizes, you can allocate
    # a large buffer just once and keep re-using it instead.
    pj = simdjson.ParsedJson(fin.read())

    pj.items('.type') #> "search_results"
    pj.items('.count') #> 2
    pj.items('.results[].username') #> ["bob", "tod"]
    pj.items('.error.message') #> "All good captain"


simdjson requires AVX2 support to function. Check to see if your OS/processor supports it:

  • OS X: sysctl -a | grep machdep.cpu.leaf7_features
  • Linux: grep avx2 /proc/cpuinfo

Low-level interface

You can use the low-level simdjson Iterator interface directly, just be aware that this interface can change any time. If you depend on it you should pin to a specific version of simdjson. You may need to use this interface if you're dealing with odd JSON, such as a document with repeated non-unique keys.

with open('sample.json', 'rb') as fin:
    pj = simdjson.ParsedJson(fin.read())
    iter = simdjson.Iterator(pj)
    if iter.is_object():
        if iter.down():

Early Benchmark

Comparing the built-in json module loads on py3.7 to simdjson loads.

File json time pysimdjson time
jsonexamples/apache_builds.json 0.09916733999999999 0.074089268
jsonexamples/canada.json 5.305393378 1.6547515810000002
jsonexamples/citm_catalog.json 1.3718639709999998 1.0438697340000003
jsonexamples/github_events.json 0.04840242700000097 0.034239397999998644
jsonexamples/gsoc-2018.json 1.5382746889999996 0.9597240750000005
jsonexamples/instruments.json 0.24350973299999978 0.13639699600000021
jsonexamples/marine_ik.json 4.505123285000002 2.8965093270000004
jsonexamples/mesh.json 1.0325923849999974 0.38916503499999777
jsonexamples/mesh.pretty.json 1.7129034710000006 0.46509220500000126
jsonexamples/numbers.json 0.16577519699999854 0.04843887400000213
jsonexamples/random.json 0.6930746310000018 0.6175370539999996
jsonexamples/twitter.json 0.6069602610000011 0.41049074900000093
jsonexamples/twitterescaped.json 0.7587005720000022 0.41576198399999953
jsonexamples/update-center.json 0.5577604210000011 0.4961777420000004

Getting subsets of the document is significantly faster. For canada.json getting .type using the naive approach and the items() approach, average over N=100.

Python Time
json.loads(canada_json)['type'] 5.76244878
simdjson.loads(canada_json)['type'] 1.5984486990000004
simdjson.ParsedJson(canada_json).items('.type') 0.3949587819999998

This approach avoids creating Python objects for fields that aren't of interest. When you only care about a small part of the document, it will always be faster.

*Note that all licence references and agreements mentioned in the pysimdjson README section above are relevant to that project's source code only.